The present invention relates to resin coated particulates used in petroleum well completions, and the process through which uncoated particulates employed as substrates are resin coated. More particularly, but not by way of limitation, the present invention comprises resin coated particulates which are less reactive or interactive with the fluids utilized to convey the particulates during petroleum well completions.
It is well known in the petroleum well completions and servicing industry that phenol-formaldehydes and related resins ("plastics") are used to consolidate otherwise incompetent formations, to coat particulates for use in gravel-packing, and to coat particulates for use as proppants in hydraulic fracturing operations.
Formation consolidation techniques are well completion practices used to stabilize wellbores so that these wellbores may be prevented from collapsing. Collapsed wellbores cause decline in the production of hydrocarbons, or a reduction in the quantity of fluids injected in secondary and tertiary recovery operations. Injected fluids are used to displace hydrocarbons towards producing wellbores. By coating the formation particulates with plastics, the formation's particulates can be welded together to create a porous "casing", suitable for facilitating the flow of fluids to or from the wellbore, whichever is preferred.
Gravel packing operations are also regarded as well completion practices in which specially sized particulates are placed in the wellbore, generally in the annular region, between the formation and a wire wrapped porous mandrel. The specially sized particulates, placed in the annular region, are sized to prevent the production of formation solids during the production of formation fluids. The wire wrapped porous mandrel is used to prevent the migration of the specially sized particulates into the subsurface and surface production equipment while allowing the production of hydrocarbons. The specially sized particulates may be "plastic" coated to enhance their performance.
Hydraulic fracturing operations also utilize "plastic" coated particulates, normally employed as proppants, to enhance and maintain the relative permeability of the hydraulically induced fracture with respect to the natural permeability of the hydrocarbon bearing formation. Hydraulic fracturing operations may be considered a well completion method as well as a remedial production operation method. Formation fracturing is used to enhance the recovery rate of hydrocarbons or the fluid injection rates in secondary and tertiary recovery operations. In hydraulic fracturing operations, highly viscous fluids are used to initiate and propagate fractures in hydrocarbon bearing subterranean formations. These "frac fluids" are also used to convey the particulates which will be used to "prop" the fracture open once the fracturing fluid has lost its high viscosity and has been recovered via the wellbore. The "frac fluid" is recovered in order to make space available in the newly formed highly permeable "proppant pack" so that the production of hydrocarbons or the injection of hydrocarbon displacing fluids, whichever is preferred, is enhanced. Examples of particulates used as proppants in various hydraulic fracturing operations include sand, glass beads, ceramics, and nut shells. Each particulate has been "plastic" coated at one time or another to enhance its performance.
Patented works which acknowledge the use of plastics to coat particulates in formation consolidation, gravel-packing, and hydraulic fracturing operations include, but are certainly not limited to:
U.S. Pat. No. 2,378,817, issued on Jun. 19, 1945 to Wrightsman, et al., which discloses the use of resins, particularly phenol-formaldehyde resins to coat formation sands in hydrocarbon producing zones to prevent wellbore collapse;
U.S. Pat. No. 3,026,938, issued on Mar. 3, 1962 to Huitt, et al., which discloses the use of non-adherent proppants coated with phenol-formaldehyde resins, as well as numerous other materials for use in hydraulic fracturing operations;
U.S. Pat. Nos. 3,176,767 and 3,176,768, both issued on Apr. 6, 1965 to Brandt, et al., which disclose a method of consolidating incompetent earth formations in oil wells by coating formation sands, silts, and clays with thermosetting resins;
U.S. Pat. No. 3,237,693, issued on Mar. 1, 1966 to Huitt, et al., which discloses a method of fracturing a formation displacing novel propping agents, comprising an inert solid particle coated with a dissolvable coating, down a well and into a fracture, thereby enhancing proppant pack conductivity;
U.S. Pat. No. 3,254,717, issued on Jun. 7, 1966 to Huitt, et al., which discloses a method of impregnating seeds for use as propping agents in hydraulic fracturing operations with plastics, including phenol-formaldehyde, urea-formaldehyde, and phenolfurfural resins;
U.S. Pat. No. 3,376,930, issued on Apr. 9, 1968 to Kiel, et al., which discloses a metal-powder coated particulate useful as a proppant in hydraulic fracturing operations.
U.S. Pat. No. 3,393,736, issued on Jul. 23, 1968 to Goodwin, which discloses a well completion method whereby a casing set in an incompetent fluid bearing formation is cut, and the incompetent formation solids removed to create a cavity which is filled with a fusible thermosetting resin coated particulate set into a permeable coherent mass;
U.S. Pat. No. 3,404,735, issued on Oct. 10, 1968 to Young, et al., which discloses a method of coating sands for gravel-packing operations using, among other things, coatings comprised of phenolformaldehyde and furfuryl alcohol resins, and silanes to provide superior consolidations;
U.S. Pat. No. 3,419,073, issued on Dec. 31, 1968 to Brooks, which discloses a formation consolidation method using a variety of plastics mixed with silanes used to enhance the bond strength between the resin and the particulate;
U.S. Pat. No. 3,492,147, issued on Jan. 27, 1970 to Young, et al., which discloses the production of particulate solids used in hydraulic fracturing which are coated with an infusible resin incorporating radioactive materials employed as tracers;
U.S. Pat. No. 3,625,287, issued on Dec. 7, 1971 to Young, which discloses a plastic coated sand using silanes with epoxies and phenol-formaldehyde resins to enhance the strength and ability of the disclosed formation sands;
U.S. Pat. No. 3,659,651, issued on May 12, 1972 to Graham, which discloses the use of reinforced plastic pellets as proppants useful in hydraulic fracturing operations;
U.S. Pat. No. 3,760,880, issued on Sep. 25, 1973 to Dollarhide, which discloses formation consolidation compositions employing particulates (e.g. sand, glass beads, particulate metals, etc.) coated with any unset resin, which is formed by the reaction of an aldehyde and a low molecular weight hydroxyaryl compound (e.g. phenol-formaldehyde), and a coupling agent (e.g. certain silanes) to enhance the bond between the particulate and the resin;
U.S. Pat. No. 3,780,807, issued on Dec. 25, 1973 to Graham, et al., which discloses the use of resins and silanes to produce novel gravel packing compositions which are comprised of coated sands bridged together to form a bond capable of withstanding relatively high differential pressures;
U.S. Pat. No. 3,929,191, issued on Dec. 30, 1975 to Graham, et al., which discloses the manufacture and use of resin coated proppants for hydraulic fracturing operations, where these products might be manufactured using a cold solvent process, or a hot, melt process using a blend of one-step resole and two-step novolac resins;
U.S. Pat. No. 3,935,339, issued on Jan. 27, 1976 to Cooke, which discloses a method of coating particulate materials, such as silica sand, glass beads, seeds, and metal particulates, with a liquid thermosetting epoxy resin creating a high compressive strength material suitable for use in hydraulic fracturing operations;
U.S. Pat. No. 4,073,343, issued on Feb. 14, 1978 to Harnsberger, which discloses a method of and composition for the treatment of unconsolidated sandy formations in which formation sands are coated with a fusible material serving to prevent or reduce materially the flow of unconsolidated sandy particles to the wellbore while permitting the flow of desirable formation fluids at a substantially unimpaired rate;
U.S. Pat. No. 4,336,842, issued on Jun. 29, 1982 to Graham, et al. and later disclaimed, which discloses the use of an "activator" to reduce the fusion temperature of the resin on coated proppants, making these materials suitable for use in low temperature hydraulic fracturing operations;
U.S. Pat. No. 4,413,931, issued on Nov. 8, 1983 to McDonald, which discloses a coating for particulates, used in hydraulic fracturing, employing a two-step, curable, novolac-type phenolic resin having a majority of o-p' dimers;
U.S. Pat. No. 4,439,489, issued on Mar. 27, 1984 to Johnson, et al., which discloses a process for the preparation of coated particulates, used as proppants, whereby lubricants such as silicone liquid, mineral oil, or a bis-stearamide of a diamine, are used;
U.S. Pat. No. 4,443,347, issued on Apr. 17, 1984 to Underdown, et al., which discloses a pre-cured charge useful in hydraulic fracturing;
U.S. Pat. No. 4,518,039, issued on May 21, 1985 to Graham, et al., which discloses a method for treating subterranean formations with a heat curable particle produced by including coupling agents, such as organo-functional silanes, on the "high strength centers" and in the resin coatings;
U.S. Pat. No. 4,527,627, issued on Jul. 9, 1985 to Graham, et al., which discloses a method of acidizing fractures propped with self-consolidating resin coated particles;
U.S. Pat. No. 4,553,596, issued on Nov. 19, 1985 to Graham, et al., which discloses a method of preventing the collapse of perforation tunnels extending from a wellbore into a subterranean formation by filling the tunnels with self-consolidating resin coated particles and curing the resin coated particles into a permeable matrix;
U.S. Pat. No. 4,564,459, issued on Jan. 14, 1986 to Underdown, et al., which is an extension of U.S. Pat. No. 4,443,347 and discloses a pre-cured proppant charge useful in hydraulic fracturing;
U.S. Pat. No. 4,581,253, issued on Apr. 8, 1986 to Evans, et al., which discloses a process for preparing a pre-cured proppant charge useful in hydraulic fracturing;
U.S. Pat. No. 4,585,064, issued on Apr. 29, 1986 to Graham, et al., which discloses an improved resin coated particle suitable for use as a hydraulic fracturing proppant comprising a particulate substrate, a substantially cured inner resin coating, and a heat curable outer resin coating;
U.S. Pat. No. 4,597,991, issued on Jul. 1, 1986 to Graham, et al., which discloses a method for producing an improved particulate material for use in fracturing as a proppant and/or as a fluid loss agent and as a screening material in gravel packing comprised of heat curable particulates capable of forming a cohesive mass, the particulates comprised of a high strength center, a coupling agent chemically bound to the center with a heat curable resin coated over the center, where the coupling agents are added to both the centers and the resin;
U.S. Pat. No. 4,664,819, issued on May 12, 1987 to Glaze, et al., which is an extension of U.S. Pat. No. 4,565,459 and U.S. Pat. No. 4,443,347 and discloses a pre-cured proppant charge useful in hydraulic fracturing;
U.S. Pat. No. 4,677,187, issued on Jun. 30, 1987 to Armbruster, et al., which discloses the preparation of furfuryl alcohol-formaldehyde resins by using a water-soluble multivalent salt as the catalyst, thereby eliminating the use of an acid catalyst and the necessary attention it requires, where the useful water soluble multivalent metal salt catalysts include the multivalent ions of manganese, zinc, cadmium, magnesium, cobalt, nickel, copper, tin, iron, lead, and calcium, where the preferred catalysts are zinc acetate, lead acetate, or mixtures thereof;
U.S. Pat. No. 4,694,905, issued on Sep. 22, 1987 to Armbruster, which discloses a precured coated particle where the particles are individually coated with a cured combination of phenolic/furan resin or furan resin to form a precured resin coating on the particles, thereby substantially improving the chemical resistance of the particles over one having a straight phenolic precured coating;
U.S. Pat. No. 4,694,905 (a second embodiment), issued on Sep. 22, 1987 to Armbruster, which discloses the use of multiple resin coatings on a particulate to form a final layered coating containing the desired amount of cured resin, thereby producing a final product having a smoother, more uniform surface than particulate material having its entire resin coating applied in a single operation;
U.S. Pat. No. 4,717,594, issued on Jan. 5, 1988 to Graham, et al., which discloses an improved resin coated particle comprising a particulate substrate, a substantially cured inner resin and a heat curable outer resin coating, where the particles are suitable for use in hydraulic fracturing operations;
U.S. Pat. No. 4,722,991, issued on Feb. 2, 1988 to Armbruster, which discloses a terpolymer prepared from phenol, furfuryl alcohol, and formaldehyde wherein a substantial amount of the furfuryl alcohol is catalytically reacted by means of a water soluble multi-valent metal salt catalyst, and further wherein the reaction is carried out under essentially hydrous conditions;
U.S. Pat. No. 4,732,920, issued on Mar. 22, 1988 to Graham, et al., which discloses a particulate suitable for use in certain well completion and well stimulation operations, where the coupling agent is added to the "high strength centers" and the resin;
U.S. Pat. No. 4,785,884, issued on Nov. 22, 1988 to Armbruster, which discloses the use of an acidic catalyst in a solvent system to cure particulate materials coated with solid thermosetting resins that can consolidate and cure at temperatures below about 130.degree. F. making it suitable as a fusible proppant in low temperature hydraulic fracturing operations;
U.S. Pat. No. 4,848,470, issued on Jul. 18, 1988 to Korpics, which discloses an improved process for removing particulate material bonded together by cured phenolic resins from a wellbore using solvents containing N-N-dimethylformamide, N-methyl-2 pyrrolidone, or mixtures;
U.S. Pat. No. 4,888,240, issued on Dec. 19, 1989 to Graham, et al., which discloses a dual-coated proppant suitable for use in hydraulic fracturing operations comprising a particulate substrate, a substantially cured inner resin coating, and a fusible curable outer resin coating;
U.S. Pat. No. 4,932,714, issued on May 8, 1990 to Gibb, et al., which discloses an epoxy coated ceramic particulate useful in fracturing and gravel packing operations.
In September 1990, Nimerick, McConnell, and Samuelson presented a paper (SPE 20639) at the 65th Annual Technical Conference and Exhibition of the Society of Petroleum Engineers in which the authors address the "Compatibility of Resin-Coated Proppants (RCP) With Crosslinked Fracturing Fluids". The authors state that "some job problems have been attributed to the incompatibility of some water-base crosslinked fracturing fluids with the curable resin-coated proppant." The authors, in presenting "a study of the effects of precured and curable RCP on water-base crosslinked fracturing fluids" found that rheological properties, crosslinker concentration/distribution, and the effect on the proppant's physical properties are critical parameters in evaluating the compatibility of the RCP with crosslinked fracturing fluids. The authors principally worked with only curable RCP's (believed to be the worst case) and found that the addition of curable RCP's to fracturing fluids could delay crosslinking times by as much as 100% and that this in turn significantly and often detrimentally impacts fluid rheology and, therefore, performance.
Also, in September, 1990, Norman, Terracina, McCabe, and Nguyen presented a paper (SPE 20640) in which the authors address the "Application of Curable Resin-Coated Proppant". The authors found that by increasing the amount of crosslinker, rheology deficiencies could be corrected. If the findings of the previous paper (SPE 20639) are indicative of the amount of crosslinker lost, as much as 30% additional crosslinker might be necessary to correct the deficiency. The authors also found no rheological impact on crosslinked fracturing fluids with the addition of curable RCP's, although these findings are inconsistent with those of others in the industry. The authors did encounter interferences with fluid "breaker" additives with the addition of RCP's, where the "breakers" are oxidative persulfate type breakers.
David A. Stiles reported that curable resin coated particulates significantly and detrimentally affected the performance of fracturing fluids in his "Compatibility of Curable Resin-Coated Proppants With Breakers in Crosslinked Fracturing Fluids" at the 38th Annual Southwestern Petroleum Short Course at Lubbock, Tex.
In April, 1992, Michael A. Smith reported, at the 39th Annual Southwestern Petroleum Short Course at Lubbock, Tex. that "new resin chemistry and coating technology has increased the areas of application for resin coated proppants. Curable resins have been changed to reduce fluids interaction which results in improved compatibility and retained conductivity. The changes in curable proppants have been related to coating technology and resin chemistry. In addition to improved fluid compatibility, the changes in these coatings reduce the risk of consolidation in highly deviated or horizontal wells. Recent developments in precured resin coated proppants place these materials in the intermediate strength range of light weight ceramics but with better economics."
Smith further states that current practice is to divide curable coatings into "three general groups, curable, dual coated, and partially cured coatings." In all cases, Smith reports that "furan resin coated sand has extended the temperature and pressure application range of pre-cured resin coated sand into the ranges previously reserved for low density ceramics."
In only one place (FIG. 6), however, does Smith really address the issue of interaction between the resin coating and constituents that comprise the fracturing fluid. In this case, the furan precured particulates actually show a higher interaction with the ammonium persulfate breaker than the corresponding phenolformaldehyde resins manufactured by the company with whom Smith is employed. All Smith's company's materials show less resin-fluid interaction than those reported by his competitor, indicating that while the products Smith represents might be superior to those of his competitor, the paucity of data addressing resin-fluid interaction, and the results that are reported give evidence that the problem of resin-fluid interactions is not resolved.
As early as 1983, McDonald reported in U.S. Pat. No. 4,413,931 that "it has been thought that the reduced strength of the conventional novolac resin-bonded sand was caused by the loss of polymerization catalyst hexamethylenetetramine (HMTA) into the formation before the resin could cure." He adds that "increasing the amount of hexa in the uncured novolac has not, however, led to significant increases in compressive strength." It was McDonald's invention to define and identify a 2-step novolac type resin with the compressive strength equal to that of the one-step resole-type resins by using a novolac resin having a majority of o-p' dimers.
Additionally, although phenol-formaldehyde resins are typically used as the material of choice to coat particulate used as proppants, Acme Resin has found that the use of furan resins offers some relief as a means of limiting the reaction between the particulate coating and fracturing fluid additives. The use of furans, however, has not eliminated the coating-fluid interaction to the satisfaction of users.
In summary, the current practice in the oil field pumping services and production industry of using resin coated particulate to enhance the conductivity of fractures in hydrocarbon bearing formations has met with limited success due to the reaction of the resin coating with the additives which comprise the hydraulic fracturing fluid. More specifically, it has been found that polymer crosslinking agents, generally referred to as crosslinkers, and polymer degradation additives, generally referred to as breakers, especially those breakers regarded as "oxidative" by those skilled in the art, are the fracturing fluid additives most susceptible to reaction with the resin coatings on particulates.
It, therefore, has been found, as reported in the published works of early 1990's, that efforts to stabilize the "plastic" coats on resin coated proppants to such a degree as to minimize the interaction between the constituents comprising the resin coating and the constituents comprising the fracturing fluid have failed.
Accordingly, the present invention has been developed to provide a resin coated particulate which is less reactive or unreactive with the fluids employed to convey the particulates during well completion operations.